Fluorescent enones

As early as 1964, Corey had suggested the intermediacy of an oriented pi complex in the cycloaddition of enones (43) and soon thereafter Hammond and coworkers, on the basis of arene fluorescence quenching by dienes, suggested the possible involvement of a polar excited state complex with substantial charge transfer character (44). Since then the possibility of cycloadditions occurring through the intervention of exciplex or excimer intermediates per se or as precursors for radical ions pairs, eq. 12,... 

A study of the photochemical addition of 2,3-dimethylbut-2-ene to the furocoumarin derivatives (117-119) has sought to establish an order of reactivity for the cycloaddition of alkenes to the enone double bond. The (2+2) adduct (120) exhibits temperature dependent fluorescence. ... 

The fluorescence and phosphorescence excitation and emission spectra of commercial polypropylene and poly(4-methylpent-l-ene) are examined using a fully compensated spectrofluorimeter. The excitation spectra of the polymers are compared with the absorption spectra of model chromo-phores of those believed to be present in the polymers. The fluorescence emission is associated primarily with the presence of enone and the phosphorescence is associated with dienone impurity chromophoric units. Bromination of cold hexane extracts of the polymers reduces significantly the intensity of the fluorescence confirming the presence of ethylenic unsaturation. The behavior of the luminescent enone and dienone groups during irradiation under sunlight-simulated conditions is examined also. Possible mechanisms for the participation of these chromophoric units in the photooxidation of the polymers are discussed. 

Hexane Extraction and Bromination. Some of the fluorescent enones are extractable from the amorphous regions of the polymer matrix by cold hexane (1,13). This prpcess enables us to perform a simple chemical test for the presence of unsaturation, i.e., bromination (18). Figure 4 shows the fluorescence excitation and emission spectra of the cold hexane extract of commercial polypropylene before and after treatment with bromine. After bromination there is a significant reduction in the fluorescence intensity, confirming the presence of unsaturation. A similar result was obtained on brominating a cold hexane extract of poly-4-... 

Microwave-induced delayed fluorescence studies have provided information on the triplet states of toluene 230 and p-chloroaniline.231 Magnetic resonance saturated phosphorescence decay measurements on tyrosine,232 and cidnp studies on but-2-enone and pentan-3-one,233 1,4-benzoquinone in propanol,234 9-methylacridine,235 and the dye-sensitized photo-oxidation of phenols230 have been reported. 

Fluorescence characteristics of some common polymers have been listed [505]. Fluorescence analysis of polyolefins has been the subject of much controversy but is generally now considered to be associated with the presence of low levels of cyclic a, -unsaturated carbonyl compounds of the enone or enal type [514]. Fluorescence and phosphorescence excitation and emission of LLDPE, HDPE and mPE were reported [515]. 

Figures 1.6 and 1.7 show fluorescence and phosphorescence of polyolefins, respectively [69]. Figure 1.6 shows that fluorescence of polyolefins cannot be attributed to the presence of polynuclear aromatic hydrocarbons (e.g. naphthalene), because the positions of emitted bands differ significantly. On the other hand phosphorescence emission (Fig. 1.7) shows the presence of a,)S-unsaturated carbonyl groups. These results indicate the presence in polyolefins of enone and/or dienone chromophoric groups which are responsible for the observed luminescence.

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